1. The Field of the Invention
The present invention is in the field of upgrading heavy oil feedstocks into lower boiling, higher quality materials. More particularly, the invention relates to bimetallic catalyst precursors that can be mixed with heavy oil feedstocks to form, in situ, a hydrocracking catalyst and a method for making the catalyst precursors.
2. Related Technology
World demand for refined fossil fuels is ever-increasing and will eventually outstrip the supply of high quality crude oil. As the shortage of high quality crude oil increases, there is an increasing demand to find better ways to exploit lower quality feedstocks and extract fuel values from them.
Lower quality feedstocks are characterized by relatively high quantities of hydrocarbons that have a boiling point of 524° C. (975° F.) or higher. They also typically contain relatively high concentrations of sulfur, nitrogen and/or metals. High boiling fractions typically have a high molecular weight and/or low hydrogen/carbon ratio, an example of which is a class of complex compounds collectively referred to as “asphaltenes”. Asphaltenes are difficult to process and commonly cause fouling of conventional catalysts and hydroprocessing equipment.
Examples of lower quality feedstocks that contain relatively high concentrations of asphaltenes, sulfur, nitrogen and metals include heavy crude, oil sands bitumen, and bottom of the barrel and residuum left over from conventional refinery processes (collectively “heavy oil”). The terms “bottom of the barrel” and “residuum” (or “resid”) typically refer to atmospheric tower bottoms, which have a boiling point of at least 343° C. (650° F.), or vacuum tower bottoms, which have a boiling point of at least 524° C. (975° F.). The terms “resid pitch” and “vacuum residue” are commonly used to refer to fractions that have a boiling point of 524° C. (975° F.) or greater.
Converting heavy oil into useful end products requires extensive processing, including reducing the boiling point of the heavy oil, increasing the hydrogen-to-carbon ratio, and removing impurities such as metals, sulfur, nitrogen and carbon forming compounds.
When used with heavy oil, existing commercial catalytic hydrocracking processes become fouled or rapidly undergo catalyst deactivation. The undesirable reactions and fouling involved in hydrocracking heavy oil greatly increases the catalyst and maintenance costs of processing heavy oils, making current catalysts unsuitable for hydroprocessing heavy oil.
One promising technology for hydroprocessing heavy oils uses a hydrocarbon-soluble molybdenum salt that decomposes in the heavy oil during hydroprocessing to form, in situ, a hydroprocessing catalyst, namely molybdenum sulfide. One such process is disclosed in U.S. Pat. No. 5,578,197 to Cyr et al., which is incorporated herein by reference. Once formed in situ, the molybdenum sulfide catalyst is highly effective at breaking up asphaltenes and other complicated hydrocarbons while preventing fouling and coking.
A significant problem with commercializing oil soluble molybdenum catalysts is the cost of the catalyst. The catalyst is typically not recovered after use and is therefore a significant expense to upgrading heavy oils. Even small improvements in catalyst performance can significantly reduce the cost of hydrocracking heavy oils by reducing the amount of catalyst used and/or by increasing the output of usable fuels.
One way to reduce the cost of oil soluble molybdenum catalysts is to substitute a portion of the molybdenum with a less expensive transition metal such as cobalt, nickel, manganese, or iron. However, attempts to form oil-soluble, bimetallic salts containing molybdenum have had very little success. In current processes for manufacturing oil-soluble, bimetallic salts, the molybdenum and the second metal (e.g., cobalt) are mixed together and reacted with an organic acid. In this reaction, most or all of the second metal precipitates without forming the desired salt. The precipitated metal cannot easily be mixed with heavy oil to form a hydrocracking catalyst. Due to problems with precipitation, oil-soluble, bimetallic catalyst precursors for hydrocracking heavy oil are currently not readily available.